Development of a compact proton scanning system in Uppsala with a moveable second magnet

A scanned proton beam yields dose distributions that in most cases are superior to passively scattered proton beams and to other external radiation treatment modalities. The present paper gives a description of the scanning system that has been developed at the Svedberg Laboratory (TSL) in Uppsala. The scanning technique and the technical design are described. The solution with a small pole gap of the magnets and a moveable second magnet results in a very compact scanning head, which can therefore be incorporated in a gantry of relatively limited size. A prototype was constructed that has been used to realize various dose distributions with a scanned beam of 180 MeV protons at TSL.